Compensated tone and volume control system



June 1, 1954 I Filed Sept. 13, 1951 VOLUME VOLUME VOLUME 2 Sheets-Sheet 1 9 RESPONSE OF EAR RESPONSE OF CONVENTIONAL \AMPLIFIER LOW VOLUME LEVEL 2 SETTING SETTING a (\SETTING 2 .5 94 3 LOW VOLUME LEVEL I QESPoNsr-z OF SETTINGI I A q fl APPARENT corqamao nsspouss f" RESPONSE OF EAR Ian/era: fors- @ZMM j WW June 1, 1954 c w, CLARAS ETAL 2,680,232

' COMPENSATED TONE AND VOLUME CONTROL SYSTEM Filed Sept. 13, 1951 2 Sheets-Sheet 2 Jazz 22. far! [01' flar'as ffiadai'a Put/Efrain Patented June 1, 1954 COMPENSATED TONE AND VOLUME CONTROL SYSTEM Carl W. Claras and Theodore Wickstrom, Chicago, Ill., assignors to Revere Camera Company, Chicago, 111., a corporation of Delaware Application September 13, 1951, Serial No. 246,386

7 Claims.

Our invention relates to a compensated tone and volume control system for use in electrical sound reproducing apparatus. The invention may be used in any apparatus that converts electrical sound currents into audible sound.

As is well known, the average human ear does not have a flat response characteristic over the audible frequency range of sound energy. Apart from different cutoff frequencies at the two ends of the range for various people, the human ear is as a rule substantially more sensitive to sound at the middle frequencies than at either the low or high frequency ends of the audible range. In general, the audible range extends from around or 30 cycles per second up to as much as 15,000 or more cycles per second. For most purposes, however, the audible range may be considered roughly as extending from about 30 cycles per second up to about 10,000 or 12,000 cycles per second.

As a corollary to the above, it is found that the average human ear particularly lacks sensitivity to high and low frequencies at low volume levels. Therefore, it is desirable to provide a means in sound reproducing apparatus to accentuate the high and low frequency response when the volume is at low level. Our invention accomplishes this desirable result by means of a circuit forming a part of a combined tone and voume control system. The system is such that at normal or high volume levels the tone con- 0 trol has conventional characteristics, since the ear adequately responds to high level tones even at the high and low ends of the audible frequency spectrum.

One object of the invention, therefore, is to provide a combined tone and volume control system wherein there is provided compensation for the response characteristics of the human car at low volume levels and wherein the compensation is automatically eliminated at normal and high volume levels.

Another object is to provide such a system wherein the high frequencies and the low frequencies alternatively may be accentuated in the conventional manner.

Still another object contemplates a tone control and a volume control that function in combination to effect the desired results of the invention.

The compensated tone and volume control system embodying our invention is relatively simple and inexpensive. It consists of conventional resistor and capacitor components made with the usual commercial tolerances. The sysof the volume and tone controls.

is shown. It is understood, however, that the description and drawings are illustrative only, and are not to be taken as limiting the invention except insofar as it is limited by the claims.

In the drawings:

Fig. 1 shows curves illustrating the frequency response of the average human ear and the frequency response of a conventional electronic amplifier;

Fig. 2 shows three curves Which illustrate different response characteristics provided by our invention;

Fig. 3 is a composite frequency response curve showing -how the ear response curve and one of the Fig. 2 response curves combine to produce a gesirable response characteristic to the car, an

Fig. 4 is a schematic diagram of a system embodying our invention.

Referring to the drawings, Fig. 1 illustrates the frequency response curve of an average human car, it being noted that the ear is considerably more sensitive to the middle frequencies than to the frequencies at the high and low ends of the audible spectrum. The flat top curve in the figure is the response characteristic of a conventional amplifier.

Fig. 2 is more or less self-explanatory. It illustrates three possiblefrequency response curves of a conventional amplifier provided with the system of our invention.

Fig. 3 illustrates how one of the response characteristics of the invention combines with the response characteristic of the human ear to provide the desired response to the car. This combined response characteristic illustrates the tone compensation provided by the invention at low volume level. This characteristic is one of the main features of the invention.

Referring to Fig. 4, a practical system embodying our invention will now be described.

A suitable source of sound currents having a workable amplitude is designated by the numeral It). This source may be the output of the de tector in a radio or television receiver, or may be the output of any audio frequency stage in such devices, or any other devices, such as electric phonographs, wire and tape recorders, or any other suitable system or apparatus.

Source ID has one side grounded and its other side connected through blocking capacitor H to terminal l2 of our compensated tone and volume control system. Blocking capacitor ll preferably has a sufficiently large capacitance so that its impedance to sound currents for the entire range to be handled is low. Thus, for example, capacitor l I may have a capacitance of about .01 mi". or even larger.

A dropping resistor l3 extends between terminal l2 and a second terminal 14. Resistor l3 preferably has a moderate value for audio frequency circuits, this value in some measure being dependent upon the values use in the remainder of the system. In general, however, resistor l3 may have a value'fro'm about25,000 ohms up to as much as 250,000 ohms, or 100,000 ohms in the example illustrated. Resistor l3 forms one resistance element of a voltage divider network that is connected between terminal i2 and a ground terminal, the two input terminals of the system.

Another resistance element of the voltage divider is current resistor l5 connected between terminal i l and ground. Resistor I5 has a rather high value in comparison to resistor i3, and it is preferably about five or six times as great as resistor l3. Thus resistor 2! may range in value from 125,000 ohms up to as much as 2 megohms. In general, a desirable value for resistor i5 is about one-half megohm, or 560,000 ohms in the example illustrated.

A capacitive circuit comprising a pair of series connected capacitors l3 and I? extends between terminals i2 and [4. They shunt resistor l3 and form a part of the voltage divider circuit or network. The junction between the two capacitors is designated l8. Capacitors Hi and H are preferably about equal in value although substantial variation from this is permissible. In general, capacitors l6 and I! should have a sufficiently low value of capacitance so that the reactance of each capacitor is substantial with respect to resistor [3 at the lower part of the frequency range to be covered, while the reactance of each capacitor at the upper part of the range should be low in comparison with resistor 13. Thus capacitors i6 and 67 may each have a value of about .001 m1". Substantial variation from this figure is possible, depending upon the value of resistor I3.

In certain applications it is possible to eliminate one or the other of capacitors l6 and I? from the capacitive circuit without seriously reducing the effectiveness of the system.

A wire extends from terminal M of the voltage divider to a terminal 23 of resistor 24 in a volume control potentiometer. The opposite terminal 25 of resistor 24 is grounded. Resistor 25 thus is in shunt with current resistor [5. The volume control potentiometer also includes a wiper 26 operating over resistor 24. Wiper 26 is the high potential output terminal of the system, and it may be connected to the input of an additional amplifier or a suitable sound transducer (not shown). The other output terminal is a ground terminal. Wiper 26, of course, controls the volume level of the system, and it also reacts on the tone control part of the system. I

Resistor 24 has a high value in comparison to the values of resistors 13 and i5, and is preferably in the megohm range. Thus, as an example, resistor 24 may have a value of from about 1 megohm to as much as 4 or 5 megohms, preferably about 2 megohms. Resistor 24 may be linear or tapered, as desired, both types for use in a potentiometer being well known.

An intermediate point 21 of resistor 25 is connected through resistor 30 to junction 3|. Resistor 32 preferably has approximately the same value as resistor 13, namely, 100,000 ohms for example.

Junction point 3i is connected to ground tli'roiigh capacitor 32. This capacitor is somewhat larger in value than capacitors l3 and I1 butis of generally the same order of magnitude. Thus capacitor 32 may have a value of about .003 mi. with a variation in either direction.

A wire33 extends from junction 3! to a terminal 34 of resistor 35, this resistor forming a part of the tone control p0tentiomete1'. Resistor 35 preferably has about the same value of resistance as resistor 2t, namely 2 megohms, and it has an intermediate point 3? formed as a terminal. The tone control potentiometer has a grounded wiper 36 which operates over resistor 35 to affect the frequency response characteristics of the system. It will be noted that terminal 4-0 of resistor 35 is open, so in effect the poten tiometer is a variable resistance.

Intermediate point 31 of resistor 35 is connected to junction i8 by wire 39.

It is obvious that resistors l3, l5 and 24 form a network that may be replaced by an equivalent resistance. Thus resistor I3 would form a high potential part of such equivalent resistance. Wiper 2s provides a means for tapping off any desired potential from the other (low potential) part of the equivalent resistance.

Similarly, resistors 30 and 35 may be replaced by an equivalent variable resistance having intermediate taps to the various capacitors. Such variable resistance is connected between point 21, an intermediate point in the other part of the first equivalent resistance, and ground.

Resistors l3 and 30 are of the same order of magnitude. Similarly, resistors 24 and 35 also are of the same order, which order is greater than that of resistors i3 and 30. Resistor i5 is intermediate in value between it and 30 on one hand and resistors 24 and 35 on the other hand. Thus the values of resistors l3, l5 and 24 have values that fall in three ascending orders of magnitude.

In setting forth the respective results produced by our system, it is helpful to consider three illiiS- trative settings of the tone control potentiometer and two illustrative ranges. of the volume control potentiometer. As to the former, wiper 36 is positioned at terminal 4 0 for Setting 1, at inter-' mediate point 31 for Setting 2, and at terminal 34 for Setting 3. The illustrative settings of the volume control potentiometer are low volume level, where wiper 25 is below intermediate point 21, and normal or high volume level, where wiper 28 is above intermediate point 21.

The results provided by our compensated tonev and volume control system when the volume control potentiometer is set for low volume level will first be described. Y I

When the tone control potentiometer is in Setting 1 (wiper 35 at or near terminal 50), the;

system functions to provide the tone compensa tion that overcomes the aforesaid deficiencies of than the low and high frequencies, thereby pro-- viding an output wherein the low and high frequencies are, in effect, boosted compared to the middle frequencies. The curve of this response is labeled Setting 1 in Fig. 2. Capacitors I6, I I and 32 are largely responsible for this response characteristic.

When the tone control potentiometer is in Setting 2 (wiper 36 at intermediate point 3'1), the system functions to attenuate the middle frequencies, compared to the low frequencies, and to attenuate the high frequencies to an even greater extent. This provides a bass boost, or a bass setting of the tone control (see Fig. 2). In this instance also, capacitors I6, I! and 32 are largely responsible for the response characteristic.

When the tone control potentiometer is in Setting 3 (wiper 30 at or near terminal 34), the low and middle frequencies are attenuated to a greater extent than the high frequencies. The output characteristic, therefore, is one in which the high frequencies predominate, a treble setting of the tone control (see Fig. 2). It should be noted that capacitor 32 is short circuited to ground when the tone control is in Setting 3, and that the only substantial high frequency attenuation is that provided by the voltage divider consisting of the upper portion of resistor 24 and the resistor 30.

The results provided by our compensated tone and volume control system when the volume control potentiometer is set for normal or high volume level (wiper 2'6 above intermediate point 21) will now be described.

When the tone control potentiometer is in Setting 1, the low and middle frequencies are attenuated to a greater extent than the high frequencies. This is true because capacitors I6 and l l have relatively low reactance at the high frequencies. The output, therefore, is one in which the high frequencies predominate, a treble'setting of the tone control.

When the tone control potentiometer is in Setting 2 (wiper 36 at intermediate point 31), the high frequencies readily pass through capacitors I6 and I1 and wire 39 to ground through wiper 36. This substantially attenuates the high frequency components and provides, in effect, a bass setting of the tone control.

Setting 3 of the tone control potentiometer (wiper 36 at terminal 34) provides a characteristic substantially like that of Setting 1 at high volume. The high frequencies are attenuated less than the middle and low frequencies, thereby providing a treble setting of the tone control.

It will be noted that our system is such that at the normal or high volume settings there is no tone compensation, as in the case of low volume settings. This is desirable since, as mentioned above, the human ear adequately responds to the high and low frequencies at normal or high volume levels.

From the above description it is thought that the construction and advantages of our invention will be readily apparent to those skilled in the art. Various changes in detail may be made without departing from the spirit or losing the advantages of the invention.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A compensated tone and volume control system comprising an input voltage divider hav- 6 ing a dropping resistor, a pair of series connected capacitors in shunt with said dropping resistor, and a current resistor between the low voltage side of said dropping resistor and ground, a volume control potentiometer including a wiper and a resistor, the latter being connected be tween ground and the high side of said current resistor, a resistor and capacitor comiected in series between ground and an intermediate point on the resistor of said volume control potentiometer, a tone control potentiometer including a groundedwiper and a resistor, the, latter having one terminal connected to the junction be-, tween said series connected resistor and capacitor, the other terminalbeing open, and a conduotor extending between the junction of said series connected capacitors and an intermediate point on said tone control potentiometer resistor, the output of said system being taken between ground and the wiper of said volume control potentiometer.

2. A compensated tone and volume control system comprising an input voltage divider including a dropping resistor and a pair of series connected capacitors in shunt with said dropping resistor, a volume control potentiometer including an output wiper and a resistor, said resistor being connected between the low voltage side of said dropping resistor and ground, a resistor and capacitor connected in series between an intermediate point' on said potentiometer resistor and ground, a tone control potentiometer having a grounded wiper and a resistor having one terminal connected to the junction between said series connected resistor and capacitor, an intermediate point on the resistor of said tone control potentiometer being connected to the junction between said series connected capacitors.

3. A compensated tone and volume control system including an input voltage divider having a dropping resistor and a pair of series connected capacitors in shunt with said dropping resistor, a volume control potentiometer having an output wiper and a high value resistor, said resistor being connected between said dropping resistor and ground, a resistor comparable in value to said dropping resistor connected at one end to an intermediate point on said potentiometer resistor, a capacitor connected between ground and the other end of the resistor connected to said intermediate point, a tone control potentiometer having a grounded wiper and a resistor, said resistor being connected at one end to the junction between said capacitor and the resistor connected to said intermediate point, the junction of said series connected capacitors being connected to an intermediate point on the resistor of said tone control potentiometer.

4. A compensated tone and volume control system comprising a high potential input terminal, a first and second resistor in series between said high potential input terminal and ground of the system, a capacitive circuit connected across said first resistor, a first potentiometer having a third resistor and wiper, sai third resistor being connected to shunt with said second resistor, the said wiper forming the high potential output of the system, a fourth resistor and a capacitor connected in series between an intermediate point on said third resistor and ground, a second potentiometer including a fifth resistor and wiper, said fifth resistor having one terminal connected to the junction between the series connected fourth resistor and capacitor, a connection from the last named potentiometer wiper to ground, and a connection between an intermediate point on the fifth resistor and a point on said capacitive circuit, said last named point having a iower potentia1 than that of said high potential input terminal.

5. The combination of claim 4 wherein the first and fourth resistors are of the same order of magnitude, the third and fifth resistors are of the-same order of magnitude, with the first resistor being of a lower order of magnitude than the second resistor and the second resistor be ing of a lower order of magnitude than the third resistor.

6. The combination of claim 4 wherein said capacitive circuit and said capacitor have capacitanoe values of the same order of magnitude, each having a substantial impedance to low audio frequencies and negligible impedance to high audio frequencies.

'7. The combination of claim 4 wherein the first and fourth resistors are of the same order of magnitude, the third and fifth resistors are of the same order of magnitude, with the first resistor being of a lower order of magnitude than the second resistor and the second resistor being of a lower order of magnitude than the third resistor, and wherein said capacitive circuit and said capacitor have capacitance values of the same order of magnitude, each having a substantial impedance to low audio frequencies and negligible impedance to high audio frequencies.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date I 2,043,161 Foster June 2, 1936 20 2,578,541 Hammond .i Dec. 11, 1951 

